A conventional modular heat-radiation structure is explained referring to Japanese Laid-Open Patent Publication 111,250/2002. According to this Patent Publication, a controller includes a printed circuit board, a module mounted on the printed circuit board, a screw for fixing the module with a heat-radiation fin for radiating heat that the module generates, and a plate-like fixture provided with a hook. The fixture is inserted between the printed circuit board and the module, and is fixed to the printed circuit board by the hook; moreover, the fixture fixes the printed circuit board with the module.
According to such modular heat-radiation structure, when the module is mounted so as to float over the printed circuit board due to a reason such as improvement of its mounting efficiency, by mounting onto the printed circuit board the plate-like fixation disc sandwiched between the module and the printed circuit board, an integral unit of the heat-radiation plate fixed by the screw and the module can be supported not only by a solder-adhered portion as a modular wiring portion, but also by the whole of the plate-like fixation disc. Therefore, even if a further heavy heat-radiation plate, etc. is mounted, the weight can be distributed over the fixation disc, and the weight weighed upon the solder-adhered portion can be reduced; consequently, solder crack occurrence can be remarkably reduced. As a result, the device quality can be improved.
However, accompanying high-density mounting inside a controller, in the above modular attachment structure, due to heat generation from the bottom face of the module, a problem has occurred that, for example, deformation due to the thermal expansion of the printed circuit board is difficult to be prevented.